<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        div{
            position: absolute;
            width: 200px;
            height: 200px;
            background-color: pink;
            top:50%;
            left: 50%;
            /* translate 如果x -50% 跟父亲没关系，是走自己盒子宽度的一半 */
            transform: translate(-50%,-50%);
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>